Preheat the oven to 160C/Gas 3. Butter a 25cm springform cake tin and line the base with baking paper.

Break the chocolate into a bowl and add the butter. Rest over a pan of barely simmering water, making sure the bowl does not touch the water. Leave to melt, stirring occasionally until it’s smooth and glossy. Don’t overheat. Turn off the heat.

Carefully separate the egg whites from the yolks. Put the sugar into the egg yolks and immediately whisk until it’s pale and thick and leaves a trail on the surface for a few seconds. This takes 4-5 minutes. Gently fold into the melted chocolate.

Whisk the egg whites into soft peaks adding 2 drops of lemon juice first. The tips of the peaks should just fold over not stand upright. Gently fold the whites into the chocolate mixture using a silicon spatula, tipping it all in at once. It’s ready when it still has a slightly marbled effect. Pour into the tin and bake for 45 minutes. It will soufflé up during cooking and just crack when ready. When you take it out it will collapse a bit, but it’s supposed to. Leave to cool in the tin.

Chef Nick Nairn

Carefully remove the cake from the tin and peel off the paper. Dust with icing sugar, cut into wedges and serve with dollops of crème fraîche and the caramel sauce.

To make the caramel sauce, heat a thick-bottomed pan over a medium heat, allowing it to warm up empty. Add half the sugar. It should begin to melt as soon as it comes in contact with the bottom of the pan. As it melts, add more sugar until it’s all in. Avoid stirring yet as this will form clumps of solid sugar, but towards the end give it a careful stir if needed, until all the sugar is completely fluid. A heatproof spatula is the perfect tool.

When the melted sugar changes colour and smells of caramel (not too light but not too dark) take off the heat and stir in the cream in two or three batches. The cream will boil and cool the sugar causing it to bubble aggressively. Stir well or the trapped steam can cause the boiling hot sugar to spit across the room. Be careful as the steam will be superheated.

Place the pan back over the heat to dissolve any lumps of caramel that have formed. Serve hot or cold, but if kept warm, don’t let it become too thick (a little water can be added if needed) otherwise you may end up with toffee.